Plain old telephone systems (POTS) have been in use for some time and, because of their relatively low operating frequency, operate very compatibly with more recently introduced, concurrently provided, Asymmetric Digital Subscriber Line (ADSL) service. More recently, however, Digital Subscriber Line (DSL) service has been proposed to be provided exclusively over the communications lines previously shared with POTS service. This, so-called, “data without POTS” service continues to work well using the same communications lines previously shared with POTS service; however certain issues may arise from the provision of exclusively DSL service over previously shared communications lines that were not present when POTS service was also provided over the same communications lines.
Switched loop services such as POTS use direct current (DC) during off-hook conditions for line signaling. In addition to line signaling, a significant benefit arises from the continued presence of the direct current on the communications line, that is, the DC assists in preventing oxidation of connection or coupling points. Under normal POTS operation, approximately 20 milliamps (mA) of DC will flow through the switched loop during an off-hook condition. This direct current is used not only to signal the central office (CO) line card but also to help maintain mechanical splices (i.e. electrical connections) that are necessary and unavoidable in communication lines by inhibiting the formation of oxides or other high resistance films thereon. The current flow responsible for inhibiting oxidation is often referred to as a sealing or wetting current.
In the newly emerging environment of “data without POTS” service, absence of the previously concurrently available switched loop signaling DC creates a problem in that the mechanical splices will oxidize over a period of time and create contact problems since the low-level data signals occurring in data without POTS service do not carry enough direct current to properly inhibit oxidation. As discussed above, an example of a data without POTS application is DSL without POTS service, but may also include voice over internet protocol (VOIP) and other data transmission services that do not also include POTS service over the same communication lines or that split the POTS service from the data at an appropriate location.
While previous systems have provided partial solutions for the oxidation problem, no design has emerged to date that generally encompasses all of the desired characteristics as hereafter presented in accordance with the present invention.